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Surfactant-mediated solvothermal synthesis of CuSbS2 nanoparticles as p-type absorber material

  • Bincy John
  • G. Genifer Silvena
  • Shamima Hussain
  • M. C. Santhosh Kumar
  • A. Leo Rajesh
Original Paper
  • 34 Downloads

Abstract

The novel chalcostibite CuSbS2 had gained unique attention due to their dynamic nature as less toxic, cost-effective and earth abundant materials for the synthesis of an absorber layer in solar cell application. Herein, a facile and effective solvothermal method was used to enhance the sphere-like grain growth in the presence of polyvinylpyrrolidone (PVP) along with other precursor’s, followed by the deposition of CuSbS2 thin films using drop casting method. The synthesized nanoparticles and the deposited films were characterized for their structural, morphological, optical and electrical properties using different characterization techniques. X-ray diffraction (XRD) and Raman analysis revealed that as the amount of PVP increased, the crystallinity improved and the impurity phase formation reduced. High-resolution transmission electron microscope (HRTEM) with reduced crystallite size in the range of 2–5 nm and field emission scanning electron microscope (FESEM), exhibited sphere-shaped grains indicating the effect of PVP as surfactant for the growth of CuSbS2 nanomaterials. The average elemental composition of the nanoparticles had been determined using EDX analysis, and the result yielded Cu rich in all the samples. Optical studies using UV–Vis-NIR diffuse reflectance spectroscopy revealed that obtained CuSbS2 nanoparticles were having the absorption in the entire visible region and the direct band gap energy was in the range of 1.25 eV to 1.53 eV and that of photoluminescence spectrum gave the emission in the near IR region. The hall measurement studies showed that the deposited CuSbS2 films exhibited p-type conductivity. Devices were fabricated with the configuration of FTO/n-TiO2/p-CuSbS2/Ag, and the electrical properties were studied by recording the current- voltage (I-V) characteristics of the heterojunction device structures.

Keywords

CuSbS2 nanoparticles Solvothermal method PVP surfactant Absorber layer Heterojunction Solar energy materials 

PACS Nos.

81.07.Wx 81.16.Be 88.40.H- 

1 Introduction

Semiconducting nanocrystals have gained much attention due to their size, tunable optical properties and wide range applications in electronics, photovoltaic devices, light emitting diodes and sensors [1]. Recently, lot of research is being carried out on synthesizing nanocrystals-based solar absorption materials and formulating nanocrystalline ink in order to fabricate the thin-film semiconducting materials using the simple spin coating and drop casting method or synthesizing nanostructure thin films using solvothermal method. Thus it extends large number of advantages in cost effective and high yield production compared to traditional vacuum processing methods [2, 3, 4, 5, 6]. Copper indium gallium disulfoselenide (CIGSSe) with 15% power conversion efficiency, copper indium selenide (CuInSe2) solar cells with 10.85% efficiency and 9% efficient Cu2ZnSn(S,Se)4 nanoparticle inks-based thin films are efficient solar absorber materials due to their ideal band gap energies, direct band gap transitions and high absorption coefficients [7, 8, 9]. The scarcity of raw materials, like indium and gallium, also toxic and environmentally hazardous selenium, prevent the large-scale production of CIGSSe based solar cells [10, 11]. Besides the usage of nontoxic and earth abundant materials like zinc and tin in CZTS based solar cell, there is an open-circuit voltage limitations due to inherent complications of the material, resulting in nanocrystals-based device efficiency below 10% [9, 12, 13, 14]. In order to overcome these challenges attempts are made to synthesize a new earth abundant and less toxic CuSbS2 solar absorber material for the production of large-scale energy conversion.

The chalcostibite CuSbS2 is a direct band gap material, exhibits tunable band gap energy in the range of 1.4 to 1.6 eV with p-type conductivity and having large absorption coefficient of 105 cm−1, which match with the desired absorption range of the solar spectrum [15, 16]. CuSbS2 nanostructures including nanobricks, nanoplates, mesobelts layers, nanowires and nanoparticles have been prepared successfully by diverse methods [2, 17, 18, 19, 20]. Also different types of vacuum- and non-vacuum-based deposition techniques have been carried out to produce CuSbS2 thin films, including chemical bath deposition followed by an annealing treatment, spray pyrolysis, electro chemical deposition, sputtering, thermal evaporation and so on [21, 22, 23, 24, 25]. Devices based on the ITO/ZnO/ CuSbS2/P3HT/Pt structure exhibit a power conversion efficiency of 1.61% and that of the structure Mo/ CuSbS2/CdS/i-ZnO/n-ZnO/Al obtains the efficiency of 3.22% [26, 27].

The nanoparticles surface is modified using polyvinylpyrrolidone (PVP) which serves as a surface stabilizer, growth modifier, a dispersant and reducing agent. Its role depends on the nanoparticles growth and morphology by providing solubility in water and diverse solvents, selective surface stabilization and even access to kinetically controlled growth conditions [28]. PVP is a non-toxic, non-ionic polymer with C=O, C-N and CH2 functional groups that is widely used in nanoparticles synthesis [29, 30, 31]. Addition of PVP leads to achieve size and shape controlled synthesis of nanoparticles with large surface to volume ratio, high surface stability and appreciable changes on the morphology and optical properties of the nanomaterials.

In this work, a facile solvothermal method is followed for the synthesis of high yield sphere like CuSbS2 nanoparticles which is used as a source material for the preparation of CuSbS2 ink. Drop casting method is used as an alternative cost effective and non-vacuum-based deposition technique for the preparation of CuSbS2 thin films. The novelty of this work is to introduce the influence of polyvinylpyrrolidone (PVP) as a capping agent and the usage of ethylene glycol as solvent instead of toxic hydrazine solvent for the synthesis of CuSbS2 nanoparticles. This leads to the promising prospects of CuSbS2 nanoparticles for the production of environment friendly materials and further the deposition of CuSbS2 thin films for solar cell applications. In this work, fabrication of CuSbS2 nanoparticles-based devices with a heterostructure consisting of Glass/FTO/ TiO2/CuSbS2/Ag and the current-voltage performance of these devices in both dark and illumination conditions is studied.

2 Experimental Procedure

2.1 Chemicals

High-purity chemicals were purchased from Merck Company and used without further purification for the preparation of chalcostibite nanoparticles. Copper (II) acetate monohydrate purified [(CH3 COO)2Cu.H2O], antimony (III) chloride extra pure (SbCl3), thiourea (CH4N2S), polyvinylpyrrolidone (PVP) with a molecular weight 40,000 and ethylene glycol were the starting materials and solvent for the synthesis of CuSbS2 nanoparticles. High-purity deionized water and ethanol were used for the centrifugation and titanium tetraisopropoxide (C12H28O4Ti) and isopropyl alcohol [(CH3)2CHOH] were the chemicals for the preparation of TiO2 thin films.

2.2 Synthesis of CuSbS2 nanoparticles

CuSbS2 nanoparticles were synthesized using a simple chemical method, solvothermal which was used for the large-scale production of fine particles. In a typical reaction, 2.5 mM copper (II) acetate monohydrate, 2.5 mM antimony (III) chloride and 7.5 mM thiourea were dissolved in ethylene glycol under constant stirring for 30 min. When the chemicals were completely dissolved, the precursor solution was transferred into a teflon-lined stainless steel autoclave, placed it in a hot air oven and maintained at 230°C for 24 h. In order to introduce the effect of PVP as a stabilizing and shape directing agent for the synthesis of CuSbS2 nanoparticles, 1 g and 1.5 g along with other chemicals were added and dissolved completely in the solvent. Once the assigned time was over, the oven was allowed to reach the ambient temperature. The autoclave was taken out from the oven, and the obtained product was isolated by repeated centrifugation using deionized water and ethanol at 4000 rpm for 15 min. The collected product was gray in color and kept for drying overnight around 120°C.

2.3 Deposition of CuSbS2 thin films

CuSbS2 nanoparticles were deposited on soda lime glass substrates using drop casting deposition technique. The substrates were cleaned by sonication for 15 min each in soap solution followed by dilute HCl and finally with double distilled water. The film was fabricated by dropping the ethylene glycol dispersed CuSbS2 nanoparticles, and the deposited film was annealed at 200°C for 30 min. The deposited films were 1–4 μm in thickness, and to carry out the electrical studies of the deposited films the silver paste was used to make contact for CuSbS2 thin films.

2.4 Characterization methods

The morphology and crystallite size of the CuSbS2 nanomaterials were examined using Libra 200 transmission electron microscope (TEM, M/s Carl Zeiss, Germany) at an acceleration voltage of 200 kV and FEG with 120 kV operations. The surface structure and chemical composition analysis of the synthesized nanoparticles was carried out using FESEM with EDX (Carl Zeiss- Sigma VP). Powder XRD studies were done using XRD model: GE- X-Ray Diffraction system-XRD 3003 TT equipped with a Cu Kα-1.5406 Å radiation source, with a scan rate of 0.04°/s. Raman spectra were recorded using Renishaw in Via Raman microscope with an excitation wavelength of 785 nm near IR laser light.

To study the optical properties of the CuSbS2 nanoparticles, diffuse reflectance spectra (DRS) were recorded in a range of 2500–190 nm using JASCO UV-Vis-NIR (Model V-670) instrument with a scan speed of 2000 nm/min and the room-temperature photoluminescence spectra were taken with a PerkinElmer (Model Lambda 45). The thickness of the prepared films was measured by a step profiler (LITEMATIC VL-50) instrument. The electrical properties such as conductivity, carrier concentration, resistivity, mobility and hall coefficient of the prepared films were studied using (ECOPIA HMS 5000) Hall Effect measurement system.

2.5 Fabrication and testing of CuSbS2 nanoparticles-based devices

CuSbS2 nanoparticles-based devices with a structure of glass/FTO/TiO2/CuSbS2/Ag were fabricated as follows. Fluorine-doped tin oxide-coated glass slide (13Ω/sq.cm) was purchased from the Sigma-Aldrich and cleansed by sonication for 15 min each in soap solution followed by dilute HCl and finally with double distilled water. A TiO2 window layer (thickness: 200 nm) was deposited on FTO glass by spin coating method having the rotation speed of 4000 rpm and then annealed at 450°C for 1 h. A CuSbS2 absorber layer (thickness: 1–2 μm) was deposited on to the TiO2 layer by drop casting method. Finally, the film was coated with silver electrode (thickness: 120 nm) using vacuum thermal evaporation. The current–voltage characteristics of the heterojunction devices were recorded under standard AM 1.5 solar illuminations with an intensity of 100 mW cm−2 using Xenon lamp as the light source and Keithley Model 2450 as digital source meter.

3 Results and discussion

3.1 Structural analysis of CuSbS2 nanoparticles

The crystallinity and phase purity of the CuSbS2 nanopowders synthesized with various amounts of PVP have been confirmed using powder X-ray diffraction (XRD). The XRD patterns of the CuSbS2 nanoparticles with and without the effect of PVP are shown in Fig. 1. The pattern give well-defined intense peaks, which is in agreement with the standard JCPDS card No: 44-1417 of orthorhombic CuSbS2 unit cell with space group Pbnm (62) and lattice constant a = 14.50 Å, b = 6.019 Å, c = 3.79 Å, respectively. From the indexed spectrum, it is clear that as the amount of PVP increases, the size of the nanoparticles decreases and obtains more crystalline CuSbS2 nanoparticles. According to the Debye–Scherrer formula, the average crystallite size of the nanoparticles is determined by
$$D = \frac{K\lambda }{\beta \cos \theta }$$
(1)
where K is the Scherrer constant (K = 0.89), λ denotes the wavelength of used radiation Cu–Kα (λ = 1.5406 Å), β is the full width at half maximum of the diffraction peaks, and θ is the Bragg’s angle.
Fig. 1

XRD patterns of the synthesized CuSbS2 nanoparticles (JCPDS no. 44-1417)

Without the effect of PVP, the chalcostibite phase detects extra peaks at 2θ = 11.13°, 15.78°, 17.58°, 22.13° and 25.01° as minor phase for Sb2S3 (JCPDS no. 42-1393) [32]. As the quantity of PVP increases, peaks assigned to Sb2S3 gradually disappears and the remaining peaks attributed to CuSbS2, suggesting that Sb2S3 would be an intermediate involved in the formation of CuSbS2 [33]. Thus, the main advantage of the effect of PVP is that it increases the crystallinity as well as broadens the peak, also eliminates the secondary phases Sb2S3 and gives a complete product formation of chalcostibite nanomaterials. For materials with 1 g and 1.5 g of PVP, a complete formation of single-phase CuSbS2 is obtained and the list of intensed peaks are given by the planes of (200), (400), (111), (410), (301), (020), (220), (510), (501), (002), (521), (430), (621) and (910), respectively [34, 35, 36].

Finding the presence of Sb2S3 minor phase in XRD pattern, further phase confirmation is done by room-temperature micro-Raman analysis, in the range of 100–1200 cm−1 having laser source of 785 nm near IR region. Figure 2 gives the micro-Raman spectra of the CuSbS2 nanopowder having PVP as the capping agent. At room temperature, the structure of CuSbS2 nanoparticles is orthorhombic with space group Pbnm. Thus for orthorhombic unit cell, group theoretical treatment of the zone center phonons yield [37]
Fig. 2

Micro-Raman spectra of CuSbS2 nanoparticles with and without the effect of PVP

with four Raman active modes represented by Ag, B1g, B2g, B3g and three infrared active modes represented by B1u, B2u, B3u and Au as the inactive mode.

The Raman peak at 191 cm−1 is attributed to the formation of small amount of excessive Sb2S3 crystalline product in CuSbS2 sample [38]. Also the two peaks at 280 cm−1 and 307 cm−1 can be assigned to the symmetric modes of the SbS3 pyramid [39], whereas thin films of CuSbS2 have Raman active modes at approximately 250 cm−1, 355 cm−1 and 1102 cm−1 [40, 41] of which the peak located at 355 cm−1 is observed in this nanopowder sample. As the amount of PVP increases, the minor peaks of Sb2S3 disappear from the pattern and there exhibits a peak at 332 cm−1 of CuSbS2 which is in good agreement with the previous data [34, 42]. Thus, the influence of PVP as a capping agent stabilizes the growth and allows the formation of well-defined CuSbS2 nanoparticles.

3.2 Morphological analysis of CuSbS2 nanoparticles

The nanostructure, shape and the quality of the prepared CuSbS2 nanoparticles have been investigated using high-resolution transmission electron microscope (HRTEM). The images in Fig. 3 depict the high-resolution TEM images with and without the effect of PVP. On the basis of our analysis, these displayed patterns reveal the size and morphology of the obtained CuSbS2 nanoparticles. In these patterns, several lattice planes are identified and in each case these fringes are continuous. Figure 3(a) shows the high-resolution TEM image of CuSbS2 nanoparticle without the addition of PVP. This image suggests that the average length of these crystallites are within the range of 4.11–5.20 nm which are slightly higher than the influence of PVP. The selected area energy diffraction pattern (SAED) which is shown in Fig. 3(b) further confirms the presence of feeble and wide diffraction rings, and it represents the lattice planes of CuSbS2 nanoparticles.
Fig. 3

High-resolution transmission electron microscope (HRTEM) and Selected Area Electron Diffraction (SAED) pattern of CuSbS2 nanoparticles (a), (b) without the effect of PVP, (c), (d) 1 g of PVP, (e), (f) 1.5 g of PVP

With the addition of PVP, the size of the obtained CuSbS2 nanoparticles decreases. From Fig. 3(c, e) one can observe that as the amount of PVP increases, the average length of the crystallite decreases. Thus the effect of 1 g of PVP gives the average length within the range of 3.32–4.21 nm and that of 1.5 g of PVP obtains in the range of 1.54–3.38 nm. Further the SAED patterns that are shown in Fig. 3(d, f) indicate more clear and strong rings, and it confirms a well-crystallized CuSbS2 nanoparticle.

Determination of growth mechanism, particle size and surface morphology of the synthesized CuSbS2 nanoparticles obtained from FESEM images is shown in Fig. 4. It is observed that the influence of PVP together with the solvent ethylene glycol modifies the structure of the CuSbS2 nanoparticles. Thus it forms a large number of uniform well-defined sphere-shaped grains with reduced particle size and less agglomeration. From Fig. 4(a) it is clear that without the effect of PVP, the particles are loosely arranged with the sizes ranging from 15 to 19 nm. At the same time, as the amount of PVP increases the size of the nanoparticle decreases. Figure 4(b, c) depicts a clear picture about the role of PVP for the formation of CuSbS2 nanoparticles. With 1 g of PVP, the nanoparticles obtain the size ranging from 10 to 16 nm, whereas with 1.5 g the particle size is from 7 to 10 nm. These results conclude that PVP is acting as a surface ligand and a binder to have a great effect on the nucleation and growth of the final CuSbS2 nanoparticles [43].
Fig. 4

FESEM images of synthesized nanoparticles with different amount of PVP (a) Sample without the effect of PVP, (b) 1 g of PVP and (c) 1.5 g of PVP

3.3 Compositional analysis of CuSbS2 nanoparticles

Figure 5(a–f) illustrates the results of the constituent elements of CuSbS2 nanoparticles that are determined by the energy-dispersive spectroscopy using the energy dispersive unit connected with field emission scanning electron microscope (FESEM with EDX). The obtained pattern confirmed the chemical composition of the CuSbS2 nanoparticles. The ratio of S/(Cu+Sb) values and the weight and atomic percentage that are extracted from the EDX analysis for Cu, Sb and S are listed in Table 1. The ideal ratio of S/(Cu + Sb) is equal to be 1, whereas the calculated ratios of S/(Cu+Sb), values are 0.660,1.116 and 1.135 for without PVP, 1 g and 1.5 g of PVP, respectively. From these results, it is clear that the composition without the addition of PVP is having sulfur loss. Thus one can infer that the effect of PVP together with the solvent ethylene glycol plays a vital role in the final product formation of CuSbS2 nanoparticles.
Fig. 5

SEM with EDX images and patterns of the obtained CuSbS2 nanoparticles with different amount of PVP, (a), (b) sample without the effect of PVP, (c), (d) 1 g of PVP and (e), (f) 1.5 g of PVP

Table 1

Compositional values of the synthesized CuSbS2 nanoparticles based on the EDX analysis

Sample

Element/Series

Weight %

Atomic %

[S]/([Cu]+[Sb])

Without PVP

Cu K

47.88

45.09

 

Sb L

30.82

15.15

0.660

S K

21.30

39.76

 

1 g PVP

Cu K

32.95

29.65

 

Sb L

37.46

17.59

1.116

S K

29.59

52.76

 

1.5 g PVP

Cu K

33.83

30.10

 

Sb L

36.02

16.73

1.135

S K

30.15

53.17

 

3.4 Optical properties of CuSbS2 nanoparticles

Figure 6(a, b) shows the UV–Vis-NIR diffuse reflectance absorption and reflectance spectra of the synthesized CuSbS2 samples. Here the absorption spectra of the samples are recorded in the range of 200–1600 nm and that of the reflectance spectra were recorded in the range of 600–1600 nm using the diffuse reflectance mode having BaSO4 as reference. In absorption spectra, it is observed that the absorption begins slowly around 200 nm and increases steadily to the higher range and obtains the maximum absorption in the visible region. From Fig. 6(b) it is clear that the diffuse reflectance sharply descends from around 830 nm to the lower wavelength region. Figure 6(c) depicts the band gaps calculated from Kubelka–Munk transformations of all the samples. The Kubelka–Munk formula can be expressed by the relation
$$F\left( R \right) = \left( {1 - R} \right)^{2} /2R$$
(3)
where F(R) is the Kubelka–Munk function which corresponds to absorbance and R is the reflectance (%). The band gap energy of the samples is measured by the extrapolation of the linear portion of the graph between the modified Kubelka–Munk function [F(R) hν]2 versus photon energy (hν) where h is the Planck’s constant and ν is the frequency [20]. From the figure, it is found that the direct band gap energy of CuSbS2 nanoparticles without PVP is 1.25 eV, whereas for 1 g of PVP it is 1.33 eV and that of 1.5 g of PVP is 1.53 eV.
Fig. 6

(a, b) The room-temperature UV-visible-NIR diffuse reflectance absorption and reflectance spectra of the three different CuSbS2, (c) band gaps of CuSbS2 nanoparticles from Kubelka–Munk transformation and (d) photoluminescence spectra of CuSbS2 nanoparticles with and without the effect of PVP

The above discussed results indicate that the optimal direct band gap energy of CuSbS2 nanoparticles with and without the effect of PVP is estimated to lie between 1.25 and 1.53 eV which is in good agreement with the reported values [2, 3, 44, 45]. However, it is sure that as the amount of PVP increases, the crystallite size of the material decreases and thus the band gap energy of the materials increases. This increase in the band gap energy with decrease in the crystallite size is attributed to the quantum confinement effect of the CuSbS2 nanoparticles [46]. Figure 6(d) gives the photoluminescence spectra (PL) of the obtained CuSbS2 nanoparticles with and without the effect of PVP. Here the measurements are taken in room temperature using Xenon lamp with excitation wavelength of 520 nm. The pattern in the spectra illustrates that as the amount of PVP increases PL intensity decreases, indicating less recombination associated with electron-hole pair transition. From the close observation of emission spectra, it is clear that the maximum emission is in near IR region.

3.5 Electrical conductivity and heterojunction properties

Determination of the type of conductivity of CuSbS2 thin films on glass substrate is investigated by Hall effect measurement system. Hall measurements are taken at a constant current of 1 μA with the magnetic field of 0.59 T at room temperature. All the samples showed p-type conductivity which is useful for photovoltaic application [47]. Observed values of resistivity, conductivity, carrier concentration, mobility and hall coefficient of the CuSbS2 thin films are listed in Table 2.
Table 2

Resistivity, conductivity, carrier concentration, mobility and hall coefficient of CuSbS2 nanoparticles with and without the effect of PVP

Sample (PVP)

Resistivity ρ (Ω cm)

Conductivity σ (S cm−1)

Carrier concentration np (cm−3)

Mobility μ (cm2 V−1 s−1)

Hall coefficient RH (cm3 C−1)

Without PVP

8.19

0.122

4.37 × 1017

1.743

14.3

1 g PVP

76.33

0.0131

3.69 × 1017

0.2219

16.93

1.5 g PVP

190

5.26 × 10−3

1.38 × 1017

0.2388

45.38

The higher carrier concentration and mobility is obtained for the thin-film sample deposited using the synthesized CuSbS2 nanopowder without the addition of PVP. The presence of Sb2S3 secondary phases and the Cu-rich presence may contribute to increase the carrier concentrations. The variation in carrier concentration, mobility, and conductivity with and without the effect of PVP is shown in Fig. 7.
Fig. 7

Carrier concentration, mobility and conductivity of CuSbS2 nanoparticles with and without the effect of PVP

The p-n heterojunction devices in the structure of glass/FTO/TiO2/CuSbS2/Ag are shown in the inset of Fig. 8(c). The current–voltage characteristic curves in both dark and illumination conditions are recorded and are shown in Fig. 8. The devices exhibit a diode-like behavior with sharp turn-on voltage ~0.6 V, and the current increases as the voltage increases in the forward direction and very low flow of current in the reverse direction [23]. These results indicate the successful formation of p–n heterojunction between the CuSbS2 p-type absorber material and TiO2 n-type window layer. Enhancement in current is observed under illumination for all the samples. This is because the light irradiation excites the electrons in the valance band to conduction band and then increases the holes in the CuSbS2, which enhance the conductivity of the sample. The photovoltaic response is not able to attain due to the electron-hole recombination at the p–n junction interface and so a buffer layer can be deposited to improve the PV properties [2, 48]. The photocurrents of the samples without PVP, 1 g of PVP and 1.5 g of PVP under illuminations are 8.4 × 10−4, 6.5 × 10−3 and 9.1 × 10−3 A. The sample prepared using 1.5 g of PVP is having higher current under illumination as compared to the other samples.
Fig. 8

Current–voltage characteristics curves of CuSbS2 heterojunction devices (a) without PVP, (b) 1 g of PVP and (c) 1.5 g of PVP. The device structure is shown as inset in fig (c)

4 Conclusions

Chalcostibite CuSbS2 nanoparticles were synthesized via solvothermal method using PVP as a surfactant and ethylene glycol as a solvent, and the deposition of CuSbS2 thin films is successfully done by drop casting method. Moreover, it was clear that the effect of PVP plays a key role in the crystalline size and shape, surface morphology, chemical composition, band gap energy and electrical properties of the CuSbS2 nanoparticles. XRD pattern as well as the Raman spectra revealed that the sample synthesized using 1.5 g of PVP gave a complete product formation without significant secondary phases. Topography and the surface morphology images obtained from HRTEM and FESEM showed that well-defined sphere-shaped nanoparticles with reduced crystallite size were obtained for 1.5 g of PVP. EDX studies indicated that the formation of complete elemental composition was obtained for the same sample. The optical band gap was calculated from Kubelka–Munk transformations and 1.5 g PVP sample obtained the optimum band gap value of 1.53 eV and that with less intensity PL emission in the near IR region. The hall measurements showed p-type conductivity for all the samples with carrier concentration in the range of 1017 cm−3. CuSbS2 nanoparticles-based devices with the configuration of glass/FTO/TiO2/CuSbS2/Ag were fabricated and the current–voltage characteristics of these devices were recorded. The sample with 1.5 g of PVP showed 9.1 × 10−3 A photocurrent under illumination which was higher than the other samples. These findings clearly indicate that the CuSbS2 nanoparticles with 1.5 g of PVP are more suitable material for a p-type absorber layer in photovoltaic applications.

Notes

Acknowledgements

One of the authors Ms. Bincy John thanks the University Grants Commission of India, for providing research fellowship (Maulana Azad National Fellowship, Grant No: F1-17.1/2016-17/MANF-2015-17-KER-53161). The authors would like to thank Dr. G. Amarendra, Scientist-In-Charge, and Dr. G. M. Bhalerao, Scientist-E UGC-DAE Consortium for Scientific Research, Kalpakkam, Tamilnadu, India, for providing sophisticated instrumentation facilities.

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Copyright information

© Indian Association for the Cultivation of Science 2018

Authors and Affiliations

  1. 1.Department of PhysicsSt. Joseph’s College (Autonomous)TiruchirappalliIndia
  2. 2.UGC-DAE Consortium for Scientific ResearchTamilnaduIndia
  3. 3.Department of PhysicsNational Institute of TechnologyTiruchirappalliIndia

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